SLANESVILLE, W.Va. -- Ice Mountain, the Hampshire County peak that earned its name and a recent National Natural Landmark designation for the refrigeration effect that takes place inside a sloping mass of boulders along its base, shows signs of thawing.

Since 1983, researchers from West Virginia University have been using temperature loggers to track the temperature of air flowing from some of nearly 150 natural vents found at the base of a 60-foot-thick boulder field that extends nearly to the top of the 1,500-foot peak.

The boulder field, or talus slope in geological terms, "is a very good cold-air trap," said Dr. J. Steven Kite, the geology professor at WVU who leads the Ice Mountain monitoring program. "The talus slope provides a lot of intake area, and the R-value of having 60 feet of rock for insulation must be in the thousands."

In winter, dense, cold air sinks deep into the Oriskany sandstone talus, and ice masses form in the spaces between the rocks. "By late winter," Kite said, "everything freezes and the vents close."

As the weather warms in spring and summer, air much cooler than outside temperatures is released through the ice vents at the base of the talus slope. The ice vent section at the bottom of the slope is about 250 yards long and 30 yards wide. "It takes months for the cold air to come out," Kite said.

For the past three years, though, air blowing from the vents at the base of Ice Mountain has reached above-freezing temperatures slightly earlier than usual. And this year, a 1 degree Celsius reading was attained on April 25, more than three weeks earlier than in any other year in which Kite and his graduate students have been logging temperatures.

Having the ice gone from Ice Mountain so early "is significant," said Rodney Bartgis, state director of The Nature Conservancy in West Virginia, which has protected a 159-acre section of Ice Mountain, including the ice vent area, since 1989. "There's reason to be concerned that a warming event may be going on."

A unique community of plants normally found at much higher latitudes and elevation has thrived in rocky soil near the ice vents probably since the end of the last Ice Age, according to Bartgis.

"It's one of the most remarkable features about this site," he said.

Dwarf dogwood, a plant that ranges from Eastern Canada to Alaska and also can be found at scattered sites above 4,000 feet in West Virginia, is found at an elevation of about 750 feet at the base of Ice Mountain. The bristly rose, also known as Arctic rose and the official provincial flower of Alberta, is another Canadian and Alaskan species that can be found at Ice Mountain, along with the twinflower, another plant normally found hundreds of miles to the north. At least six boreal, or Northern, plant species can be found near the base of Ice Mountain.

"Although this place and the plants that live here have likely persisted since the end of the Pleistocene [about 11,700 years ago], there is no promise that it will remain as it is through the coming decades," Bartgis said.

Kite said a lack of historic scientific data on Ice Mountain's natural refrigeration system makes it difficult to determine just how significant the current warming trend might be.

There are accounts of local residents being able to find ice in the mountain's base vents as late in the year as September during the 1800s. At church picnics during that era, Ice Mountain ice was used to cool lemonade and crank out homemade ice cream. Civil War soldiers are said to have used the larger vents to store food.

"At one time, the ice may have lasted the entire year," Kite said, "but it seems to be formed seasonally now."

Kite said the earliest reliable temperature record taken at an ice vent on the Hampshire County peak he is aware of took place on an August day in the 1960s, when a reading of 3.5 degrees Celsius, or about 38 degrees Fahrenheit, was recorded. "In August, during the years I've been coming here, I've never seen anything lower than 7 degrees Celsius, or about 45 degrees Fahrenheit," he said.

Air flowing from the mountain's base vents is, on average, about 15 degrees cooler than outside air temperatures. Kite said there are days in late April and May when it can be nearly 60 degrees cooler.

On a visit to the site last week, Kite recorded an air temperature reading of 45 degrees Fahrenheit inside a large vent, while the air temperature a short distance away from the opening was 60 degrees. Cool air was flowing out of the vent at the rate of 1.5 mph.

While Ice Mountain's unique ecosystem might have survived 10,000 years of climate fluctuations so far, Bartgis said, "we need to take steps to help make sure this unique place stays resilient" in the face of forest pests, invasive species and a warming planet. "The world's changing more quickly, with more stressors," he said.

While greenhouse gas emissions need to be addressed, he said, attention also should be given to controlling deer browsing, invasive plants, damaging pests and other things that cause stress to plants living in Ice Mountain's low-temperature microclimate.

The Nature Conservancy is treating shade-giving hemlock trees to keep them free from the hemlock woolly adelgid, an invasive insect that is decimating hemlock stands across the Eastern United States. To avoid compacting soil and damaging rare plants, visitation at the Ice Mountain Preserve is limited to docent-led hikes along established trails. Hikes can be arranged by visiting www.nature.org/icemountain.

"Setting aside a place like this is important," Bartgis said, "but it doesn't mean the conservation work is done."

Ice Mountain is the 14th National Natural Landmark to be designated in West Virginia, and the first site in the Mountain State to become a part of the National Park Service-administered program since the 1970s. National Natural Landmarks must have unique biological or geological features, and pass a scientific panel's evaluation process and a peer review. The National Natural Landmark program includes 593 sites.

During a ceremony Thursday in the North River Mills United Methodist Church, adjacent to the preserve, Beth Johnson, director of the National Park Service's Resource Stewardship and Science program, presented a plaque bearing the preserve's new landmark status to Nature Conservancy officials.